DESCRIPTION: (Applicant's Description) In collaboration with the biostatisticians and staff in Core B, Core C is a service facility with 2 major objectives: (1) assist in providing study subjects for all three projects utilizing epidemiologic methodology appropriate to the aims of each project; (2) provide epidemiological consultation and expertise during the set-up and design, fieldwork, data analysis, and interpretation of the public health and risk implications for manuscript preparation. The centralized nature of these activities will help ensure that valid, consistent, and reliable data and biological samples will be collected and processed, duplication of effort will be avoided, and facilitate sharing of resources and subject information to meet the different demands of each project. These tasks will be especially pertinent since the project leaders are laboratory scientists.